1. Field of the Invention
The proposed invention relates to a method for integrating an anti-reflection layer and a salicide block, and more particularly to a method for simplifying fabricating process of a photodetector device.
2. Description of the Prior Art
Because of advancement of semiconductor technology and the gradually increased requirement of high-integrated devices, the importance of a device that includes several different functional elements is increased, such as the photodetector device that includes a photodiode and a transistor. However, because any specific functional element corresponds to a specific structure and a specific fabricating process, inconsistent difficulties is unavoidable during integration of different elements, especially when the structure of any element is complex, such as complementary metal-oxide semiconductor. A popular solution of the difficulty is to divide the whole device into several independent parts and then to form each part separately. For instance, a chip is divided into several parts and when any specific part is formed photoresist is used to cover other parts. Obviously, unavoidable disadvantages of this method comprise prolonged cycle time and increased wastage of interactants.
In terms of a photodetector device that is usually used by a digital camera and scanner, as the basic structural illustration shown in FIG. 1A, the photodetector device is formed on substrate 10 and comprises sensor area 11 and transistor area 12. Herein, several isolations 102 are located on substrate 10, some doped regions 101 are located in the sensor area and are separated from each other by some isolations 102, and there are transistors made of gates 121, sources 122, drains 123 and spacers 124 located in the transistor area. And silicide 125 locates on gates 121, sources 122 and drains 123. Besides, dielectric layer 13 locates on substrate 10 and covers all forementioned structures, interconnects 14 locates on dielectric layer 13 and further connects with transistors, covering layer 15 locates on dielectric layer 13 and totally covers interconnects 14, and color filter 16 locates on covering layer 15 and over doped regions 101. Further, because color filter 16 is used to let only some specific light propagate to specific doped regions 101, not only is at least one color filter located over any doped region 101, but also there is no light restrictive structure, such as interconnect 14 located between a doped region 101 and corresponding color filter 16.
However, in sensor area 11, because the light that propagates through color filters 16 to doped regions 101 will be partly reflected and also owing to the fact that light does not always vertically propagate to doped regions 101, reflected light will be distributed in all directions. Significantly, as reflected light is reflected by light restrictive interconnects 14, it is possible that any doped region 101 is interfered with by other doped regions 101 and then crosstalk phenomena occurs. This means that any doped region 101 cannot distinguish between received light as being the light propagated from corresponding color filter 16 or the light propagated from neighboring interconnects 14 which only is noise. Therefore, as FIG. 1B shows, to make sure any doped region 101 is not interfered with by light that is reflected by other doped regions 101, it is necessary to form anti-reflection layer 17 on all doped regions 101 before dielectric layer 13 is formed. As usual, available materials of anti-reflection layer 17 are TiN, Ti or TiW.
On the other hand, in transistor area 12, importance of silicide 125 is increased as critical scale is decreased, but it is not desired to cover total transistor area 12 by silicide 125. That is to say, it is necessary to form salicide block 18 on substrate 10 and cover the forbidden region of transistor area 12 before silicide 125 is formed, as FIG. 1B shows, where the forbidden region is the region in which silicide 125 is not required. In general, material of the salicide block 18 will not react with metal for forming silicide 25, and available materials comprise tetraethyl-orthosilicate (TEOS).
According to the previous discussion, it is natural that because the material of anti-reflection layer 17 is different from the material of salicide block 18, through doped regions 101 and isolations 102 of both areas can be formed together to simplify the fabricating process of the photodetector device, but the following processes of different areas cannot be formed at the same time until silicide 125 is formed. However, and referring to FIG. 1B, due to the structural difference of the two areas, some processes for constructing these different structures are always incompatible, such as the process for forming gate 121, the process for forming silicide 125 and the process for forming color filter 16. But due to the location of the anti-reflection layer as being similar to the location of salicide block 18, it is possible to integrate the process for forming anti-reflection layer 17 and the process for forming silicide block 18. Thus, overcoming current difficulties to properly integrate these processes is an important field of fabrication processes of the photodetector device.
A principal object of the present invention is to provide a method for integrating the fabricating processes of anti-reflection layer and the fabricating processes of the salicide block.
Another object of the present invention is to provide a method for forming both the anti-reflection layer and the salicide block at the same time.
A further object of the present invention is to provide a method in which the anti-reflection layer and the salicide block are made of identical materials.
Still an object of the invention is to provide a manufacturable and practical method for forming both the anti-reflection layer and the salicide block.
Objects of the invention further includes a method for forming a photodetector device, where anti-reflection layer for preventing crosstalk phenomena and a salicide block for making sure the location of silicide are formed together to simplify the fabricating process and to improve efficiency.
In short, a preferred embodiment of the present invention is a method which comprises: Providing a substrate that is divided into at least a sensor area and a transistor area, wherein the sensor area comprises a doped region and the transistor area comprises a transistor that includes a gate, a source and a drain; forming a composite layer on the substrate, wherein the composite layer at least also covers both the sensor area and the transistor area, and the composite layer increases the refractive index of light that propagates from the doped region into the composite layer; performing an etching process and a photolithography process to remove part of the composite layer and to let top of the gate, the source and the drain not being covered by the composite layer; and performing a salicide process to let top of the gate, the source and the drain being covered by a silicate.
Further, when the embodiment is applied to form a photodetector device, the following steps are included: Removing some leftover interacts of the salicide process; forming a first dielectric layer on both the composite layer and the silicide layer; forming some interconnects on the first dielectric layer, wherein interconnects locate over both transistors and isolations; forming a second dielectric layer on the first dielectric layer, wherein the second dielectric layer also covers the interconnects; and forming some color filters on the second dielectric layer, wherein the color filters locate over these doped regions.
Obviously, one main characteristic of the invention is that the composite layer is used as an anti-reflection layer of the sensor area and a salicide block of the transistor region at the same time. Thus, after doped regions and transistors are all formed, it is possible to integrate the fabricating processes of the anti-reflection layer and the fabricating processes of the salicide block. Further, the composite layer is made of several alternate overlapped basic layers and the refractive index of any basic layer is different from refractive indexes of adjacent basic layers.